The British Home Secretary, Mr Jack Straw, must decide by next Wednesday whether to allow the Spanish request for the extradition of Gen Augusto Pinochet to go before the courts.
That political hand-grenade landed on Mr Straw's desk following yesterday's historic ruling by the law lords that the former Chilean dictator does not have immunity from arrest to face charges of genocide, torture and terrorism.
In Chile, pro-Pinochet activists vented their anger on reporters, calling them "sons of whores", and Gen Pinochet's son denounced the verdict as a "sadistic and cruel blow".
Chile's President, Mr Eduardo Frei, vowed to contest the ruling, and said he planned to send the Foreign Minister, Mr Jose Miguel Insulza, to Europe to back up his government's arguments against the British decision. Mr Frei later called a meeting of the National Security Council as the army called for the release of Gen Pinochet.
In Santiago last night, police closed access to the main central square, where protesters gather. Marchers faced down police with water cannon and tear gas. At least two people suffered broken bones and an unknown number were arrested.
The Chilean ambassador in London, Mr Mario Artaza, called on Mr Straw to make his final decision quickly. "We are not here to protect the dictator of yesterday, we are here to protect and defend our transition to democracy," he said.
In a landmark judgment - which brought gasps of astonishment from the public gallery, and tears of joy for anti-Pinochet campaigners in the street outside - Lord Nicholls, one of the three judges who voted to overturn the earlier High Court ruling, said: "International law has made plain that certain types of conduct, including torture and hostage-taking, are not acceptable conduct on the part of anyone.
"This applies as much to heads of state, or even more so, as it does to everyone else. The contrary conclusion would make a mockery of international law."
Also rejecting the reasoning of the High Court, Lord Steyn said that if no lines were drawn it followed "that when Hitler ordered `the final' solution his act must be regarded as an official act deriving from the exercise of his functions as head of state."
Legal experts welcomed the lords' three to two decision as "a coming of age" for international law.
Downing Street would say only that due process of law was being observed. Mr Straw would now act in a quasi-judicial role in considering the Spanish request in line with the 1989 Extradition Act, and it was stressed his decision would not be a political one.
But the political problem for Mr Straw and the government was immediately clear as ministers considered the diplomatic fallout from yesterday's ruling, as well as its implications for Anglo-Chilean relations, while Baroness Thatcher led Tory calls for Senator Pinochet's return to Chile on compassionate grounds. The Conservative leader, Mr William Hague, backed Lady Thatcher's view.
The former dictator heard the news as he celebrated his 83rd birthday at the private London clinic where he is recovering from back surgery. He had obviously hoped to complete his celebrations at home - with an ambulance ready yesterday afternoon to whisk him to a waiting jet and a flight to Chile.
If Mr Straw allows the extradition case to proceed, the legal process - which could lead all the way back to the House of Lords - could keep Senator Pinochet in Britain for years.
In Geneva, the UN High Commissioner for Human Rights, Mrs Mary Robinson, said the decision "will hearten human rights defenders around the world".
In France, politicians on all sides of parliament applauded the verdict and relatives of victims of Chile's "dirty war" popped open bottles of champagne.
"Let justice be done," said President Jacques Chirac.
Ms Isabel Allende, whose father Salvador was toppled by Gen Pinochet, hailed the ruling as "marvellous".
Gen Pinochet is calm and composed and will fight attempts to extradite him, one of his supporters said in London.
There was a broad welcome in Ireland for the law lords' ruling. The chairman of the Oireachtas Justice Committee, Mr Eoin Ryan TD, said the case against Gen Pinochet was "overwhelming".
--(Additional reporting: Reuters, AFP)